Preheat the oven to 200C/400F/Gas 6.
For the crepes, whisk together the flour and eggs, adding enough milk to make a batter the consistency of double cream.
Heat a crepe pan and melt a small knob of butter.
Ladle enough crepe mixture into the pan to thinly and evenly coat the pan and cook for one to two minutes per side.
Remove the crepe and place onto a sheet of kitchen towel. Repeat with the remaining batter.
For the filling, beat the egg yolks with the sugar and fold in the prunes and oranges.
In a clean bowl, whisk the egg whites until stiff. Fold this into the yolk mixture.
Line the crepes up on a baking tray and equally divide the filling mixture onto one half of each crepe. Fold each empty side over to create half-moon shapes.
Place in the oven for eight to ten minutes, or until puffed up.
Transfer to plates and serve warm.